1. Field of the Invention
This invention relates to transparent recording materials suitable for use in facilitating feeding in copying and printing devices. Specifically, it relates to coatings for transparencies having specific physical properties for use in overhead projectors.
2. Description of Related Art
Many different types of transparent image receptive sheets or receptors are known in the art. Typically, these transparent sheets are comprised of thin films of one or more organic resins such as polyesters, overcoated with an image receptive layer on one side, and sometimes on both sides. They can be used as receptors for different printing and imaging methods, such as thermal transfer printing, ink-jet printing and plain paper copying to produce transparencies suitable for use with commercially available overhead projectors.
In thermal mass transfer imaging or printing, an image is formed on a receptor sheet when a donor sheet or ribbon is brought in intimate contact with the receptor sheet and heated. Colored material to be transferred from the donor is selected by a thermal printhead having small, electrically heated elements operated by signals from a computer, and the material is transferred to areas of the receptor sheet in an image-wise manner. A full colored image is generated in at least 3 passes comprising yellow, cyan and magenta print cycles. In the formation and development of xerographic images, a toner composition comprised of resin particles and pigment particles is generally applied to a latent image generated on a photoconductive member. Thereafter, the image is transferred to a receptor and affixed there, by the application of heat, pressure, or a combination thereof. In either the printing or copying process, the image receptive sheets are fed through the respective devices either singly or continuously from a stack. During continuous feeding, multiple feeding tendencies are present, usually leading to jams, unless the image receptors specifically incorporate some feeding aids either in the image receptive layer or as a coating on the side of the receptor opposite the imaging side to facilitate feeding. In some cases, a backing sheet is used to facilitate this feeding process.
U.S. Pat. No. 5,200,254 (Henry et al) discloses a receptor sheet manifold for thermal mass transfer imaging comprising a polymeric image receptor sheet and a non-transparent backing sheet attached thereto. The image receptor sheet has a substrate film having an image receptive layer coated on at least one surface thereof. The image receptive layer comprises an imaging polymer, a perfluoroalkylsulfonamidopolyether antistatic agent and silica particles. The non-transparent backing sheet has a contact surface touching the receptor sheet of the manifold, and an opposing surface having a coating composition comprising a resin binder, an antistatic agent or agents, and a particulate, such that this opposing surface has a Bekk smoothness of about 450 to about 550 Bekk seconds.
Japanese Patent No. 1289838A discloses a composite polyester film having a cover layer comprising a concentration of sulfonic acid or sulfonate on at least one surface. The composite film is taught to eliminate "pile traveling" (simultaneous feeding of more than one sheet), and yield excellent transparency flatness, and easy toner adhesion.
U.S. Pat. No. 4,480,003 discloses a transparency film for use in plain paper electrostatic copiers. The base of the transparency film is a flexible, transparent, heat resistant polymeric film. An image receiving layer, preferably, a toner-receptive, thermoplastic, transparent polymethyl methacrylate polymer containing dispersed silica particles is coated On a first major surface of the polymeric film. On the second major surface of the film base is coated a layer of non-migratory electrically conductive material, preferably a polymer derived from the reaction of pyridine and 2 amino-pyridine with partially chloromethylated polystyrene. It is preferred that a primer coating be interposed between the polymeric film base and the layer of conductive material to provide suitable adhesion of the coating to the film base. It is also preferred that the layer of conductive material be over-coated with a protective coating having additives to control abrasion, resistance, roughness and slip properties. It is disclosed that the sheet can be fed smoothly from a stack and produces clear background areas.
U.S. Pat. No. 5,104,721 discloses a medium for electrophotographic printing or copying comprising a polymeric substrate coated with a polymeric coating having a Tukon hardness of about 0.5 to 5.0 and a glass transition temperature of about 5.degree. to 45.degree. C. The coating comprises at least one pigment which provides a coefficient of static friction of from 0.20 to 0.80 and a coefficient of dynamic friction of from 0.10 to 0.40. The medium has improved image quality and toner adhesion. It is particularly useful in laser electrophotographic printing. The polymer employed in the coating can contain thermosetting or thermoplastic resins, and preferably aqueous acrylic emulsions such as Rhoplex.TM. resins from Rohm and Haas.
U.S. Pat. No. 5,104,731 discloses a dry toner imaging film media having good toner affinity, anti-static properties, embossing resistance and good feedability through electrophotographic copies and printers. The media comprises a suitable polymeric substrate with an antistatic matrix layer coated thereon. The matrix layer has resistance to blocking at 78.degree. C. after 30 minutes and a surface resistivity of from about 1.times.10.sup.8 to about 1.times.10.sup.4 ohms per square at 20.degree. C. and 50% relative humidity. The matrix contains one or more thermoplastic polymers having a T.sub.g of 5.degree. C. to 75.degree. C., and at least one crosslinked polymer which is resistant to hot roll fuser embossing, at least one of the polymers being electrically conductive.
U.S. Pat. No. 4,684,561 discloses a multilayer color sheet for thermal transfer printing comprising a substrate having a colorant layer on one side of the substrate and a resin layer formed on the other side of the substrate. The resin layer comprises fine particles of a solid material, at least one lubricating material and a polymer resin so that the resin layer is made irregular on the surface thereof due to the presence of the fine particles. The anti-stick effect can be developed more effectively when using two or more surface active agents, liquid lubricants and solid lubricants in composition. The fine particles may be made of various materials, such as metals, inorganic materials and organic materials. Preferred particles include synthetic amorphous silica, carbon black, alumina titanium oxide, calcium silicate, aluminum silicate and the like.
Although there are a host of image receptive coatings disclosed in the art, the means for facilitating feeding from a stack is disclosed in only a few instances. In some of these instances, the coating is coated on a backing sheet, rather than on the imaging receptor, and to be remove after imaging, so that it will not interfere with the projected image. The choice of coatings is therefore not severely restricted, and low haze coatings are not required. Thus, there remains a need for low haze coatings that can be coated directly onto the non-imaging surface of the receptor to aid in stack feeding, thus eliminating the use of backing sheets, especially for use with thermal mass printers.
The present inventors have now discovered a class of polymers that can be coated from an aqueous medium onto the non-imaging side of a receptor to facilitate stack feeding.